Hafler 1K trimpot fried - how do I replace? - diyAudio
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Old 14th August 2007, 11:03 AM   #1
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Default Hafler 1K trimpot fried - how do I replace?

I have recently refreshed/restored my Hafler XL-280 power amp and upon powering up with a series lightbulb and a variac, I noticed that the bias trimpot on one side appeared to be very erratic in its operation. After some fiddling, I powered down and gave the trimpot 10-15 turns from stop to stop to loosen it up and clean the contacts.
When I turned the amp back on the bias was very, very low (about 50mA at full ine voltage) and the trimpot did absolutely nothing no matter how mutch I turned it. I assume the trimpot is fried - the bias was almost 200mA at 60 volts AC before I tried to loosen it up - that was too high, now it's stuck low...

When I looked on digikey and Mouser, I found nothing. This is a 1000 Ohm single turn / side adjust with a 10mm spacing between the legs. I think the wiper is 5mm offset to the rear. Everything I find is 5mm spacing with 2.5mm offset.

Anyone have any suggestions? Is wirewound Ok or only Cermet?

Anyone want to sell a Hafler 1K trimpot?
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Old 14th August 2007, 11:55 AM   #2
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Wish I could see, but I suspect that you're not being creative enough.

If the holes are too far apart, I've occasionally lengthened the leads on the trimpot with leads cut from a resistor.

Use your noggin. Shouldn't be too tough to come up with a fix.
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Old 14th August 2007, 01:09 PM   #3
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wirewound=bad idea..... wirewounds have a "jumpy" response, and the resistance changes in steps. you want a pot with a smooth response and continuously variable for a bias pot
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